A program is proposed to study the cellular events responsible for the initiation of sporulation in Bacillus subtilis. This study centers around the use of mutants blocked in various steps of the sporulation process. These mutants define the genetic loci involved in the determination of the cell to differentiate into a spore. Analysis of the repressor fraction from cells at various stages of sporulation and in mutants unable to sporulate is a major goal of these studies. The repressor fraction is isolated by affinity chromatography on DNA cellulose and analyzed by analytical polyacrylamide gel electrophoresis. Differences in number and kind of protein molecules in this fraction have been noted and the effect of these proteins on transcription by RNA polymerase is being investigated.